FIRST LAYER OR UPPER LAYER WELDING SECTION OF HIGH Cr STEEL TURBINE ROTOR, OVERLAY WELDING MATERIAL FOR WELDING SECTION, AND METHOD FOR MANUFACTURING OVERLAY WELDING SECTION

ABSTRACT

The present invention relates to a multilayer overlay welding section in which a first layer of an overlay welding section to be formed on the bearing contact surface of a high Cr steel turbine rotor includes C: 0.05 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.5%, Cr: 4.0 to 7.7%, and Mo: 0.5 to 1.5% with a remainder including Fe and unavoidable impurities, a multilayer overlay welding section in which, in addition to the above layer, an upper layer welding section includes C: 0.05 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 2.5%, Cr: 1.0 to 4.0%, and Mo: 0.5 to 1.5%, and a welding material therefor and a process for producing the multilayer overlay welding section.

TECHNICAL FIELD

The present invention relates to a multilayer overlay for forming aCr-containing steel overlay on a surface with which bearings of a highCr steel turbine rotor come into contact.

BACKGROUND ART

Since a high Cr steel is excellent in high-temperature strength andlow-temperature toughness, the steel has been increasingly used as amaterial for high-pressure and medium-pressure turbine rotors ofgenerators. However, the contact surface with the bearings of the highCr steel turbine rotor is prone to develop seizure at the bearingsduring its use, so that there is a concern of inviting damage.Therefore, there has been proposed a method for preventing thegeneration of seizure by overlay welding a low alloy steel on thebearing part of the rotor (e.g., see Patent Document 1).

Heretofore, with regard to such a kind of overlay welding, mainlywelding materials and welding methods for submerge arc welding have beendeveloped.

For example, Patent Document 2 proposes a welding material to be appliedto a journal part of a turbine rotor and, in consideration of weldresidual stress, discloses one using a welding material having lowstrength and large linear expansion coefficient as a first layer weldingmaterial as compared with a low alloy steel of an upper layer and arotor substrate.

Moreover, in the invention described in Patent Document 3, it isintended to reduce a difference in the level of strength for the purposeof an increase in fatigue strength. Patent Document 4 disclosesintention of an improvement in fatigue strength by using a weldingmaterial having a high Cr content as a first layer.

BACKGROUND ART DOCUMENT Patent Document

-   Patent Document 1: JP-A-57-137456-   Patent Document 2: JP-A-6-272503-   Patent Document 3: JP-A-9-76091-   Patent Document 4: JP-A-9-066388

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

However, since the welding material used in the first layer weldingmaterial described in Patent Document 2 contains no Cr, accumulation ofstrain occurs in the first layer at shape discontinuous parts such as athrust part during stress relief annealing and there is a possibility ofgeneration of defects such as cracks in some cases, depending on thestrength of the upper layer.

Also, in the execution with the welding material having a Cr amount of1.0% for the first layer defined in the invention described in PatentDocument 3, there is a concern that the Cr content of the weldingsection decreases and further there is a concern that diffusion of C andthe like occurs and the strength at the welding metal side decreases dueto the difference in the Cr amount between the base material and thewelding metal during the stress relief annealing after welding.

As above, in the conventional technologies, since the Cr content of thewelding material which comes into contact with the rotor substrate islow and strength balance among the rotor substrate, the first layer, andthe upper layer is not considered, the residual stress induced bywelding is high. Also, in the shape discontinuous parts such as thethrust part at which stress concentration is prone to occur due to theshape, there is a concern of occurrence of defects. In Patent Document4, although a welding material having a high Cr content is used for thefirst layer, it is supposed that stress relief annealing cracksusceptibility increases through component dilution by welding dependingon the components of the rotor base material, so that there is room forimprovement.

Accordingly, an object of the present invention is to provide acombination of overlay welding materials for the first layer or theupper layer and a first layer or upper layer welding section obtainedtherefrom, and a process for producing a multilayer overlay weldingsection, which satisfy the strength and toughness required for a high Crsteel turbine rotor bearing part and are used for avoiding cracks duringthe stress relief annealing.

Means for Solving the Problems

Namely, a first invention relates to a first layer welding section amonga multilayer overlay welding section formed on a bearing contact surfaceof a high Cr steel turbine rotor, and the first layer welding sectionincludes, in terms of % by weight: C: 0.05 to 0.2%, Si: 0.1 to 1.0%, Mn:0.3 to 1.5%, Cr: 4.0 to 7.7%, and Mo: 0.5 to 1.5%, with a remainderincluding Fe and unavoidable impurities, in which the unavoidableimpurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% orless, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% orless, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weightbased on the first layer welding section.

A second invention relates to the first layer welding section among themultilayer overlay welding section formed on the bearing contact surfaceof the high Cr steel turbine rotor, and in the first invention, thefollowing expression (1) is satisfied:

Pcr(1)=(a Cr amount in the first layer welding section)×0.65−(a Cramount of the high Cr steel turbine rotor−the Cr amount in the firstlayer welding section)×0.35>0.7  (1).

A third invention relates to an overlay welding material for a firstlayer welding section for obtaining the first layer welding sectionaccording to the first or second invention, among the multilayer overlaywelding section formed on the bearing contact surface of the high Crsteel turbine rotor, and the welding material includes, in terms of % byweight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.2%, Cr: 2.0 to5.5%, and Mo: 0.1 to 1.5%, with a remainder including Fe and unavoidableimpurities, in which the unavoidable impurities contain P: 0.015% orless, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and asum of one or more kinds selected from the group consisting of Ni, Nband Ti is 0.2% or less in terms of % by weight based on the overlaywelding material for the first layer welding section.

A fourth invention relates to an upper layer welding section formed onthe first layer welding section according to the first or secondinvention, among the multilayer overlay welding section formed on thebearing contact surface of the high Cr steel turbine rotor, the upperlayer welding section includes, in terms of % by weight: C: 0.05 to0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 2.5%, Cr: 1.0 to 4.0%, and Mo: 0.5 to1.5%, with a remainder including Fe and unavoidable impurities, in whichthe unavoidable impurities contain P: 0.015% or less, S: 0.015% or less,Cu: 0.2% or less, V: 0.15% or less, Ni: 0.3% or less, and Nb: 0.07% orless in terms of % by weight based on the upper layer welding section.

A fifth invention relates to the upper layer welding section of the highCr steel turbine rotor, and in the fourth invention, an amount of Vcontained in the upper layer welding section is smaller than an amountof V contained in the first layer welding section according to the firstor second invention.

A sixth invention relates to the upper layer welding section of the highCr steel turbine rotor, and in the fourth or fifth invention, thefollowing expression (2) is satisfied:

Per(n)=(a Cr amount in the upper layer welding section at n-thlayer)×0.65−{a Cr amount in the upper layer welding section at (n−1)-thlayer−the Cr amount in the upper layer welding section at the n-thlayer}×0.35>0.7  (2),

in which when N represents the number of layers constituting themultilayer overlay welding section, 2≦n≦N.

A seventh invention relates to an overlay welding material for an upperlayer welding section for obtaining the upper layer welding sectionaccording to any one of the fourth to sixth inventions formed on thefirst layer welding section of the multilayer overlay welding sectionformed on the bearing contact surface of the high Cr steel turbinerotor, and the welding material includes, in terms of % by weight: C:0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 3.0%, Cr: 1.0 to 2.5%, and Mo:0.1 to 1.5%, with a remainder including Fe and unavoidable impurities,in which the unavoidable impurities contain P: 0.015% or less, S: 0.015%or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or morekinds selected from the group consisting of Ni, Nb and Ti is 0.2% orless in terms of % by weight based on the overlay welding material forthe upper layer welding section.

A eighth invention relates to a process for producing a multilayeroverlay welding section of a high Cr steel turbine rotor, the processincluding:

forming the first layer welding section according to the first or secondinvention on the bearing contact surface of the high Cr steel turbinerotor by welding using an overlay welding material for the first layerwelding section including, in terms of % by weight: C: 0.03 to 0.2%, Si:0.1 to 1.0%, Mn: 0.3 to 1.2%, Cr: 2.0 to 5.5%, and Mo: 0.1 to 1.5%, witha remainder including Fe and unavoidable impurities, in which theunavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu:0.2% or less, and V: 0.1% or less, and a sum of one or more kindsselected from the group consisting of Ni, Nb and Ti is 0.2% or less interms of % by weight based on the overlay welding material for the firstlayer welding section, and

forming the upper layer welding section according to any one of thefourth to sixth inventions on an upper layer of the thus-formed firstlayer welding section by welding using an overlay welding material forthe upper layer welding section including, in terms of % by weight: C:0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 3.0%, Cr: 1.0 to 2.5%, and Mo:0.1 to 1.5%, with a remainder including Fe and unavoidable impurities,in which the unavoidable impurities contain P: 0.015% or less, S: 0.015%or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or morekinds selected from the group consisting of Ni, Nb and Ti is 0.2% orless in terms of % by weight based on the overlay welding material forthe upper layer welding section.

Advantage of the Invention

According to the upper layer welding section of the present invention,ferrite is not formed at the boundary part between the first layer andthe upper layer, also it is possible to suppress stress relief annealingcracks, and bearings can be prevented from seizing with satisfyingstrength and toughness required for the bearing part.

Furthermore, the strength balance among the base material, the firstlayer, and the upper layer is made most suitable by combining the firstlayer welding section according to the first invention and the secondinvention as mentioned above with the upper layer welding section, sothat the strain concentration to the first layer can be prevented duringstress relief annealing. Thereby, the execution becomes possible withoutgenerating stress relief annealing cracks even for the welding of thethrust part which may develop large residual stress at welding. Also, byconsidering the difference in the Cr amount in each layer, anoverlay-strengthened high Cr steel turbine rotor having stable qualitycan be provided with preventing the formation of pro-eutectoid ferrite.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing an outline of a high Cr steel turbinerotor in the invention.

FIG. 2 is a schematic view showing an analysis portion to be measured atthe time of property evaluation of inside of a first layer weldingsection or an upper layer welding section and a sampling position of atest piece for a high-temperature low strain rate tensile test.

FIG. 3 is a graph showing a relationship between the Cr amount andreduction of area at a high-temperature low strain rate tensile testusing Cr variation materials.

FIGS. 4( a) to 4(d) are schematic views showing a ring crack test piecefor evaluating stress relief annealing crack susceptibility at the firstlayer welding section. FIG. 4( a) is a drawing showing a samplingposition of the test piece for use in the test. FIG. 4( b) is a sideview of the test piece. FIG. 4( c) is a front view of the test piece.FIG. 4( d) is an enlarged view of the A part in FIG. 4( c). The unit ofvalues of the sizes in FIGS. 4( a) to 4(d) is “mm”.

FIG. 5 is a schematic view showing a step of imparting tensile residualstress to a U notch bottom part at the time of conducting the ring cracktest.

FIG. 6 is a schematic view showing the shape of the test piece for ahigh-temperature low strain rate tensile test. The unit of values of thesizes in FIG. 6 is “mm”.

MODE FOR CARRYING OUT THE INVENTION

The following will describe embodiments of the present invention indetail but the invention is not limited thereto and can be implementedin any variations.

<First Layer Welding Section>

The components of the first layer welding section according to theinvention contain C: 0.05 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.5%, Cr:4.0 to 7.7%, and Mo: 0.5 to 1.5% in terms of % by weight and a remainderincludes Fe and unavoidable impurities. The following will describe themeanings of these components and, when the first layer welding sectionhas the above-mentioned composition, a difference in the level ofstrength among the base material and the overlay first layer orsubsequent overlay layers can be suppressed to a degree at whichproblems do not practically arise and thus stress relief annealingcracks in the first layer can be suppressed. The contents in thefollowing are all shown in terms of % by weight.

C: 0.05 to 0.2%

Since C is a necessary additive element from the viewpoint of securingthe tensile strength of the welding section, a lower limit thereof isset to 0.05%. On the other hand, in view of a decrease in an impactvalue and an increase in weld crack susceptibility, an upper limitthereof is set to 0.2%.

Si: 0.1 to 1.0%

Since Si is an element necessary as a deoxidizer or for securingstrength, a lower limit thereof is set to 0.1%. However, since anexcessive content of Si promotes cracks such as stress relief annealingcracks and invites a decrease in toughness, an upper limit thereof isset to 1.0%. For the same reason, the lower limit thereof is preferablyset to 0.25% and the upper limit is desirably set to 0.7%.

Mn: 0.3 to 1.5%

Since Mn is an element necessary as a deoxidizer or for securingstrength similarly to Si, a lower limit thereof is set to 0.3%. However,since an excessive content of Mn invites a decrease in toughness, anupper limit thereof is set to 1.5%. For the same reason, the upper limitis set to desirably 1.2%, more desirably 1.0%.

Cr: 4.0 to 7.7%

Cr is an important element for securing strength and toughness. In orderto suppress the strain concentration to the first layer, suppress thedifference in Cr from the base material, and prevent the formation offerrite, a lower limit thereof is set to 4.0%. However, since anexcessive content of Cr increases hardenability and enhances weld cracksusceptibility, an upper limit thereof is set to 7.7%. For the samereason, the upper limit is desirably set to 6.7%.

Mo: 0.5 to 1.5%

Since Mo precipitates as a carbide during the stress relief annealingand enhances temper softening resistance, it is an important element forobtaining strength after the stress relief annealing. In order tosuppress the strain concentration during the stress relief annealing, alower limit thereof is set to 0.5%. However, since an excessive contentof Mo enhances cracking ability and invites a decrease in toughness, anupper limit thereof is set to 1.5%. For the same reason, the upper limitis desirably set to 1.0%.

The essential constituting elements of the first layer welding sectionare as mentioned above. Also, the remainder substantially contains Feand unavoidable impurities resulting from dilution from the basematerial. As the unavoidable impurities, the first layer welding sectionmay contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V:0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W:1.5% or less, and Nb: 0.07% or less in terms of % by weight based on thewhole first layer welding section. The following will describe reasonsthereof.

P: 0.015% or less

P is an impurity element that mixes in from a raw material during thesmelting of a metal material. Since P has a possibility of decreasingtoughness, it is desirable to reduce it as far as possible. Therefore,the content of P is set to 0.015% or less.

S: 0.015% or less

Similarly to P, S is an impurity element that mixes in from a rawmaterial during the smelting of a metal material. Since S has apossibility of decreasing toughness, it is desirable to reduce it as faras possible. Therefore, the content of S is set to 0.015% or less.

Cu: 0.2% or less

Since Cu has a possibility of decreasing the toughness of the weldingsection, an upper limit of the content is set to 0.2% or less.

V: 0.2% or less

V is known as an element for increasing the temper softening resistanceto obtain strength after stress relief annealing. However, from thestudies of the present inventors, it has been found that V extremelyelevates the stress relief annealing crack susceptibility. Therefore,the content of V is limited to 0.2%, preferably 0.1% at most.

Ni: 0.3% or less

Since an excessive content of Ni has a possibility of causing temperembrittlement, the content of Ni is limited to 0.3% at most.

Co: 1.5% or less

In the case where the base material contains Co, the content of Coshould be suppressed to an increase by dilution/fusion from the basematerial during welding and is limited to 1.5% at most.

B: 0.005% or lessW: 1.5% or lessNb: 0.07% or less

These elements are generally known as elements that improve tempersoftening resistance during the stress relief annealing and secureroom-temperature strength. However, from the studies of the presentinventors, it has been found that an excessive content of each elementdecreases toughness and also degrades welding ability. Therefore, in theinvention, as for the contents of these components, upper limits aredetermined to the above values, respectively.

The Cr amount contained in the first layer welding section according tothe invention preferably satisfies the following expression (1):

Pcr(1)=(Cr amount in first layer welding section)×0.65−(Cr amount inhigh Cr steel turbine rotor−Cr amount in first layer weldingsection)×0.35>0.7  (1)

With an increase in the Cr content of the first layer welding sectionand a decrease in the difference from the Cr amount in the high Cr steelturbine rotor, the ferrite formation during the stress relief annealingis suppressed. When the Pcr (1) value represented by the aboveexpression (1) is a value exceeding 0.7, the ferrite formation issuppressed at the boundary between the base material and the first layerwelding section and an overlay-strengthened high Cr steel turbine rotorhaving stable quality can be obtained. Incidentally, the Cr amounts inthe above expression (1) are all represented in terms of % by weight.

<Welding Material for First Layer Welding Section>

In the welding material for obtaining the above first layer weldingsection, the dilution of the components occurs with the base materialduring the overlay welding on the base material and also the dilution ofthe components occurs with the upper layer to be welded on the upperlayer. The dilution of the components occurs through the fusion of apart of the neighboring layers during welding and the migration of thecomponents from a layer having high concentration of the components to alayer having low concentration thereof. It is generally sufficient thatthe base material is a high Cr steel to be commonly used as a turbinerotor for thermal power generation and particularly, the materialthereof is preferably 12Cr steel, more preferably one so-called new 12Crsteel in which W, Co, and B are added thereto.

With considering the aforementioned dilution, the welding material forthe first layer welding section is defined for obtaining the abovecomposition of the first layer welding section. Thereby, the action andeffect of the first layer welding section can be exhibited.

By using the welding material for the first layer welding section as anoverlay first layer in the high Cr rotor substrate, a difference in thelevel of strength between the base material and the overlay first layeror subsequent overlay layers can be suppressed to a degree at which noproblem arises practically and the stress relief annealing cracks can besuppressed in the first layer. Moreover, for the welding material, bysuppressing the difference in the Cr content between the base materialand the first layer welding metal so that the first layer weldingsection satisfies the above expression (1), the formation of ferrite canbe suppressed.

Specifically, the welding material for the first layer welding sectionaccording to the invention includes C: 0.03 to 0.2%, Si: 0.1 to 1.0%,Mn: 0.3 to 1.2%, Cr: 2.0 to 5.5%, and Mo: 0.1 to 1.5% in terms of % byweight, and the remainder includes Fe and unavoidable impurities. Theunavoidable impurities are desirably P: 0.015% or less, S: 0.015% orless, Cu: 0.2% or less, and V: 0.1% or less, and the sum of one or morekinds selected from the group consisting of Ni, Nb, and Ti is 0.2% orless in terms of % by weight based on the welding material for the firstlayer welding section.

The following will specifically describe individual components.

C: 0.03 to 0.2%

The C content of the first layer welding section according to theinvention ranges from 0.05 to 0.2% and there is a case where the basematerial component exceeds the upper limit of the C content range of thefirst layer welding section. In consideration of the dilution/fusionwith the base material component during welding, it is desirable that alower limit of the C content in the welding material is set to 0.03% andan upper limit thereof is set to 0.2% in view of welding workability andthe like, for making the C content of the first layer welding sectionfall within the above range.

Si: 0.1 to 1.0%

The Si content of the first layer welding section according to theinvention ranges from 0.1 to 1.0%. In consideration of thedilution/fusion with the base material component during welding, the Sicontent in the welding material desirably ranges from 0.1 to 1.0%, formaking the Si content of the first layer welding section fall within theabove range.

Mn: 0.3 to 1.2%

The Mn content of the first layer welding section according to theinvention ranges from 0.3 to 1.5% and there is a case where the basematerial component exceeds the upper limit of the Mn content range ofthe first layer welding section. In consideration of the dilution/fusionwith the base material component during welding, it is desirable that alower limit of the Mn content in the welding material is 0.3% forassuring the effect as a deoxidizer and an upper limit thereof is 1.2%so as not to exceed the upper limit of the component range of the firstlayer welding section.

Cr: 2.0 to 5.5%

The Cr content of the first layer welding section according to theinvention ranges from 4.0 to 7.7%. In consideration of thedilution/fusion with the base material component during welding, the Crcontent in the welding material desirably ranges from 2.0 to 5.5% forobtaining the component range of the first layer welding section.

Mo: 0.1 to 1.5%

The Mo content of the first layer welding section according to theinvention ranges from 0.5 to 1.5%. In consideration of thedilution/fusion with the base material component during welding, the Mocontent in the welding material desirably ranges from 0.5 to 1.5% forobtaining the component range of the first layer welding section.

As the impurities contained in the welding material, there may bementioned P, S, Cu, V, Ni, Nb, Ti, W, Co, B, and the like.

As the impurities of the first layer welding section defined in theinvention, the following are allowed: P: 0.015% or less, S: 0.015% orless, and Cu: 0.2% or less. These are components that deterioratemechanical properties and welding ability of both the welding sectionand base material and, also in the welding material for the first layer,the same component range is desirable as that of the first layer weldingsection.

V: 0.1% or less

V is a component contained in the base material. For obtaining therange, i.e., 0.2% or less, of the first layer welding section accordingto the invention, the V content in the welding material is desirably0.1% or less in consideration of the dilution/fusion during welding.

The sum of one or more kinds selected from the group consisting of Ni,Nb, and Ti being 0.2% or less

Ni and Nb are elements contained in the base material. For obtaining Ni:0.3% or less and Nb: 0.07% or less that are the ranges of the firstlayer welding section according to the invention, the contents thereofin the welding material are desirably as low as possible inconsideration of the dilution/fusion during welding.

Moreover, Ti is an element that is usually hardly contained in the basematerial. However, since Ti increases the formation of non-metalinclusion when remains, the content thereof in the welding material isdesirably as low as possible. Therefore, the sum of one or more kindsselected from the group consisting of Ni, Nb, and Ti is desirably 0.2%or less.

W, Co, and B are components that may be contained in the base material.For obtaining W: 1.5% or less, Co: 1.5% or less, and B: 0.005% or lessthat are the ranges of the first layer welding section according to theinvention, the contents thereof are desirably as low as possible withinthe ranges unavoidably contained by a usual process for producing thewelding material.

<Upper Layer Welding Section>

The components constituting the upper layer according to the inventioncontain C: 0.05 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 2.5%, Cr: 1.0 to4.0%, and Mo: 0.5 to 1.5% in terms of % by weight and the remainderincludes Fe and unavoidable impurities.

The following will describe reasons for defining the components of theupper layer welding section of the invention. Incidentally, the contentsin the following are all represented in terms of % by weight.

C: 0.05 to 0.2%

Since C is a necessary additive element for imparting a necessarystrength to the bearing surface, a lower limit thereof is set to 0.05%.However, since the impact value is lowered and the weld cracksusceptibility becomes high when the content thereof exceeds 0.2%, anupper limit thereof is set to 0.2%.

Si: 0.1 to 1.0%

Since Si is an element necessary as a deoxidizer or for securingstrength as shown in the first layer overlay welding metal, the contentthereof is limited to 0.1% at least. However, since an excessive contentof Si promotes cracks such as stress relief annealing cracks and invitesa decrease in toughness, an upper limit thereof is set to 1.0%. For thesame reason, the lower limit is desirably set to 0.3% and the upperlimit is desirably set to 0.7%.

Mn: 0.3 to 2.5%

Since Mn is an element necessary as a deoxidizer or for securingstrength similarly to Si, a lower limit thereof is set to 0.3%. However,since an excessive content of Mn invites a decrease in toughness, anupper limit thereof is set to 2.5%. For the same reason, the lower limitis desirably set to 0.7% and the upper limit is desirably set to 2.0%,and further, the lower limit is more desirably set to 1.0%.

Cr: 1.0 to 4.0%

Cr is an important element for securing strength and toughness. In orderto suppress the difference in Cr from the first layer and prevent theformation of ferrite, a lower limit thereof is set to 1.0%. However,since strain is concentrated to the first layer owing to too highstrength when the content exceeds 4.0% and a crack may be generated insome cases during the stress relief annealing, an upper limit thereof isset to 4.0%.

Mo: 0.5 to 1.5%

Since Mo precipitates as a carbide during the stress relief annealingand enhances temper softening resistance, it is an important element forobtaining strength after the stress relief annealing. In order tosuppress the strain concentration during the stress relief annealing, alower limit thereof is set to 0.5%. However, an excessive contentthereof enhances the stress relief annealing crack susceptibility andinvites a decrease in toughness, an upper limit thereof is set to 1.5%.

The essential constituting elements of the upper layer welding sectionare as mentioned above and the remainder substantially contains Fe.However, minute amounts of unavoidable impurities such as S, P, and Nimay be further contained in the range where the above properties are notinhibited. Seizure resistance can be made excellent by using the aboveupper layer welding section as an upper layer in the high Cr steelturbine rotor substrate, and the formation of ferrite can be suppressedby suppressing the difference in the Cr content between the first layerand the upper layer welding section.

As the unavoidable impurities, there may be contained P: 0.015% or less,S: 0.015% or less, Cu: 0.2% or less, V: 0.15% or less, Ni: 0.3% or less,and Nb: 0.07% or less in terms of % by weight based on the upper layerwelding section. The following will describe details.

P: 0.015% or less

P is an impurity element that mixes in from a raw material during thesmelting of a metal material. Since P has a possibility of decreasingtoughness, it is desirable to reduce it as far as possible. Therefore,the content of P is set to 0.015% or less.

S: 0.015% or less

S is also an impurity element that mixes in from a raw material duringthe smelting of a metal material. Since S has a possibility ofdecreasing toughness, it is desirable to reduce it as far as possible.Therefore, the content of S is set to 0.015% or less.

Cu: 0.2% or less

Since Cu has a possibility of decreasing the toughness of the weldingsection, an upper limit thereof is set to 0.2% or less.

V: 0.15% or less

V is an element for increasing the temper softening resistance to obtainstrength after the stress relief annealing. On the other hand, in thecase of considering that the prevention of the stress annealing crack isimportant, the content of V is limited. Since V improves the tempersoftening resistance, the strain concentration to the first layer occursand thus a crack may be generated during the stress annealing in somecases. In order to avoid it, the V content is limited to 0.15% or less.

Incidentally, a welding material containing more than 0.15% of V may beused in combination, for example, with avoiding the stress annealingcracks by controlling the V content of the welding section to 0.15% orless using a welding material having a low V content as the first layerof the upper layer and with controlling the V content of the weldingsection of each of the second and subsequent layers or at least theproduct surface layer part that is the outermost surface of the upperlayer to 0.15 to 0.3%. In that case, the Cr content of welding sectionof the product surface layer part is desirably 2.5% or less forpreventing seizure. Although a mechanism between the Cr amount and thegeneration of seizure is not solved, it is empirically well known forone of ordinary skill in the art that a risk of the generation ofseizure becomes high when the Cr amount exceeds 2.5%.

Moreover, the amount of V contained in the upper layer welding sectionis preferably smaller than the amount of V contained in the first layerwelding section from the viewpoint of no occurrence of excessive stressconcentration to the first layer.

Ni: 0.3% or less

Since an excessive content of Ni has a possibility of causing temperembrittlement, the content thereof is limited to 0.3% at most.

Nb: 0.07% or less

Nb improves the temper softening resistance during the stress reliefannealing and secures the room-temperature strength. However, since anexcessive content thereof may decrease toughness and also degradewelding ability, an upper limit thereof is defined to be 0.07% in theinvention.

The Cr amount contained in the upper layer welding section preferablysatisfies the following expression (2):

Pcr(n)=(Cr amount in upper layer welding section at n-th layer)×0.65−{Cramount of upper layer welding section at (n−1)-th layer−Cr amount ofupper layer welding section at n-th layer}×0.35>0.7  (2),

in which when N represents the number of layers constituting themultilayer overlay welding section, 2≦n≦N.

By controlling Pcr (n) represented by the above expression (2) to avalue exceeding 0.7 with considering the difference between the Cramount of the upper layer welding section at the n-th layer and the Cramount of the upper layer welding section at the (n−1)-th layer, theferrite formation at the boundaries of individual layers is suppressed.In this regard, Per (2) means a calculation value satisfying theexpression (2) of an upper layer that is the 2nd layer (the 1st layer ofthe upper layer) on the first layer welding section that is the 1stlayer. In this case, in the expression (2), the upper layer weldingsection at the (n−1)-th layer corresponds the first layer weldingsection. Incidentally, the Cr amounts in the above expression are allrepresented in terms of % by weight.

<Overlay Welding Material for Upper Layer Welding Section>

With considering composition variation by the occurrence of dilution ofthe components with the first layer welding section during the overlaywelding on the first layer welding section, the overlay welding materialfor obtaining the above upper layer welding section is defined forobtaining the above composition of the upper layer welding section. Bythe welding using the overlay welding material, the above upper layerwelding section can be obtained, and the action and effect of satisfyingstrength and toughness and avoiding cracks during the stress reliefannealing can be exhibited.

Specifically, the overlay welding material for the upper layer weldingsection contains C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 3.0%, Cr:1.0 to 2.5%, and Mo: 0.1 to 1.5% in terms of % by weight, with theremainder including Fe and unavoidable impurities. The unavoidableimpurities desirably contains P: 0.015% or less, S: 0.015% or less, Cu:0.2% or less, and V: 0.1% or less, and the sum of one or more kindsselected from the group consisting of Ni, Nb, and Ti is 0.2% or less interms of % by weight based on the overlay welding material for the upperlayer welding section.

The following will specifically describe the above components.

C: 0.03 to 0.2%

The C content of the upper layer welding section according to theinvention ranges from 0.05 to 0.2%. In consideration of thedilution/fusion with C contained in the first layer welding sectionaccording to the invention, it is desirable that a lower limit of the Ccontent in the welding material is set to 0.03% and an upper limitthereof is set to 0.2% in view of welding workability, in order not toexceed the upper limit of the C component range of the upper layerwelding section.

Si: 0.1 to 1.0%

The Si content of the upper layer welding section according to theinvention ranges from 0.1 to 1.0%. In consideration of thedilution/fusion with Si contained in the first layer welding sectionaccording to the invention, the Si content in the welding materialdesirably ranges from 0.1 to 1.0% for obtaining the Si component rangeof the upper layer welding section.

Mn: 0.3 to 3.0%

The Mn content of the upper layer welding section according to theinvention ranges from 0.3 to 2.5%. In consideration of thedilution/fusion with Mn contained in the first layer welding sectionaccording to the invention, the Mn content in the welding material isdesirably ranges from 0.3% to 3.0% for obtaining the Mn component rangeof the upper layer welding section.

Cr: 1.0 to 2.5%

The Cr content of the upper layer welding section according to theinvention ranges from 1.0 to 4.0%. In consideration of thedilution/fusion with Cr contained in the first layer welding sectionaccording to the invention, a lower limit of the Cr content in thewelding material is desirably 1.0% so as not to be lower than the lowerlimit of the Cr content of the upper layer welding section. An upperlimit thereof is desirably 2.5% so as not to exceed the upper limit ofthe Cr content of the upper layer welding section.

Moreover, the Cr content of the upper welding section as the productsurface layer part that is the outermost surface of the upper layer isalso desirably 2.5% or less for preventing seizure. Similarly, an upperlimit of the overlay welding material for the upper layer weldingsection as the product surface layer part is also desirably 2.5%.

Mo: 0.1 to 1.5%

The Mo content of the upper layer welding section according to theinvention ranges from 0.5 to 1.5%. In consideration of thedilution/fusion with Mo contained in the first layer welding sectionaccording to the invention, the Mo content in the welding materialdesirably ranges from 0.1 to 1.5% for obtaining the component range ofthe upper layer welding section.

Unavoidable impurities: P, S, Cu, V, Ni, Nb, Ti, W, Co, B

As the impurities contained in the upper layer overlay welding materialaccording to the invention, the following are allowed: P: 0.015% orless, S: 0.015% or less, and Cu: 0.2% or less in terms of % by weightbased on the overlay welding material for the upper layer weldingsection. These are components deteriorating mechanical properties andwelding ability, and the same component ranges are desirable as those ofthe upper layer welding section according to the invention.

V: 0.1% or less

As for V, 0.2% or less of V may be contained in the first layer weldingsection by the dilution/fusion from the base material. Therefore, forobtaining 0.15% or less as the range of the V content of the upper layerwelding section according to the invention, the V content in the weldingmaterial is desirably 0.1% or less in consideration of thedilution/fusion during binding.

The sum of one or more kinds selected from the group consisting of Ni,Nb, and Ti being 0.2% or less

Ni and Nb are elements that may be contained in the base material. Forobtaining Ni: 0.3% or less and Nb: 0.07% or less that are the ranges ofthe upper layer welding section defined in the invention, the contentsthereof in the welding material are desirably as low as possible.

Moreover, Ti is usually hardly contained in the base material but, sinceTi increases the formation of non-metal inclusion when remains in thewelding section, the content in the welding material is also desirablyas low as possible. Therefore, the sum of one or more kinds selectedfrom the group consisting of Ni, Nb, and Ti is desirably 0.2% or less.

W, Co, and B may be contained in the ranges of W: 1.5% or less, Co: 1.5%or less, and B: 0.005% or less in the first layer welding section by thedilution/fusion from the base material. However, the upper layer weldingsection does not necessarily contain these components and, in view ofcosts, it is sufficient that the contents fall within the rangesunavoidably contained by a usual process for producing the weldingmaterial.

With regard to the composition of the welding section, since thematerial to be welded is generally melted to a degree of 20 to 40% andis diluted/fused with the welding material during welding, the elementalcomposition of the welding material may be determined with taking thedilution/fusion into account.

<High Cr Steel Turbine Rotor>

In the invention of the present application, a high Cr steel turbinerotor is a target of the overlay welding. The high Cr steel turbinerotor is constituted by a high Cr steel and, for example, a steelcontaining 8 to 13% of Cr is exemplified. The composition of the turbinerotor in the invention is not limited to specific one and a high Crsteel capable of being used as the turbine rotor is sufficient.

The following will exemplify a typical turbine rotor composition (% byweight).

C: 0.05 to 0.25%,

Si: 1.0% or less,

Mn: 1.5% or less,

Ni: 1.0% or less,

Cr: 8 to 13%,

Mo: 2.0% or less,

V: 0.05 to 0.4%,

Nb: 0.01 to 0.1%,

N: 0.01 to 0.05%,

W: 0.05 to 5.0%,

Co: 0.05 to 5.0%, and

B: 0.015% or less,

with the remainder being Fe and unavoidable impurities.

FIG. 1 is a schematic view showing a side surface of a high Cr steelturbine rotor to which the overlay welding material according to theinvention is applied. For example, a steel containing 8 to 13% by weightof Cr is exemplified.

A high Cr steel turbine rotor 1 has a journal part 2 and a thrust part 3as bearing parts, and the overlay welding section can be formed bywelding to one or both of the journal part 2 and the thrust part 3 usingthe welding material according to the invention.

At the formation of the overlay welding section, it is desirable to formthe first layer welding section according to the invention and then toform the upper layer welding section thereon using the welding materialaccording to the invention. In the formation of the above first layerand upper layer welding sections, it is desirable to perform the weldingby TIG (Tungsten Inert Gas) welding, submerge arc welding, or the like.The welding method and welding conditions in the welding are notparticularly limited in the invention and a known method can beconducted under known conditions.

At the welding of an under layer, it is desirable to determine the Crcontent of the first layer so as to satisfy the following expression(1).

Pcr(1)=(Cr content in first layer welding section)×0.65−(Cr content ofhigh Cr steel turbine rotor−Cr content in first layer weldingsection)×0.35>0.7  (1)

Also, at the welding of overlaying, it is desirable to determine the Crcontent of the upper layer so as to satisfy the following expression(2).

Pcr(n)=(Cr content in upper layer welding section at n-thlayer)×0.65−{Cr content in upper layer welding section at (n−1)-thlayer−Cr content in upper layer welding section at n-thlayer}×0.35>0.7  (2),

in which when N represents the number of layers constituting themultilayer overlay welding section, 2≦n≦N.

EXAMPLES

The following will describe Examples of the invention.

Using a 12Cr rotor substrate having a component composition (theremainder being Fe and unavoidable impurities) shown in Table 1 on thesupposition of a high Cr steel turbine rotor, overlay welding wires eachhaving the component composition (the remainder being Fe and unavoidableimpurities) shown in Table 2 were used as welding materials for firstlayer welding sections of Examples or Comparative Examples and further,overlay welding wires each having the component composition (theremainder being Fe and unavoidable impurities) shown in Table 3 wereused as overlay welding materials for upper layer welding sections ofExamples or Comparative Examples.

The component analysis of the rotor substrate was conducted inaccordance with the prescription of JIS G 1253 (2010) after a test piecewas sampled from an arbitrary portion. The component analysis of theoverlay welding wires as the overlay welding materials for the firstlayer welding section or for the upper layer welding object wasconducted in accordance with the prescription of JIS Z 3317 (2010).

Using each of the above welding materials, the first layer and the upperlayer was overlay-welded by TIG welding under the welding conditionsshown in Table 4. Thereafter, a test piece was sampled from the checkanalysis position 20 shown in FIG. 2 and the component analysis (checkanalysis; the remainder being Fe and unavoidable impurities) of thefirst layer and upper layer welding sections was conducted. Thecomponent analysis of individual welding sections was conducted inaccordance with the prescription of JIS G 1253 (2010).

Furthermore, as shown by α in FIG. 2, a tensile test piece was sampledfrom each test piece so that the first layer welding metal becamecentral. After the piece was held at a temperature of 660° C. for 30minutes to homogenize the temperature, which simulates a stress reliefannealing process, a high-temperature low strain rate tensile test wasperformed at a strain rate of 6.7×10⁻⁶/s. A value of reduction in area(%) was used for evaluation.

TABLE 1 12Cr rotor substrate composition (% by weight) C Si Mn P S Ni CrCu Mo V Nb N W Co B 0.10 0.07 0.08 0.010 0.0014 0.22 9.71 0.03 0.60 0.200.05 0.0145 1.80 3.00 0.010

TABLE 2 Overlay welding wire for first layer (% by weight) Wire Ni + No.C Si Mn P S Cu Ni Cr Mo V Nb Ti Nb + Ti 1 0.10 0.76 1.40 0.012 0.0120.24 0.01 0.02 <0.01 — — — 0.01 2 0.01 0.02 0.44 0.012 0.008 — — — — — —— — 3 0.10 0.36 0.77 0.006 0.009 0.19 0.06 2.29 1.11 0.01 — 0.002 0.06 40.04 0.51 1.06 0.005 0.010 0.11 0.02 2.36 1.05 — — — 0.02 5 0.12 0.170.41 0.003 0.006 0.16 0.02 2.31 1.06 0.27 0.036 — 0.06 6 0.08 0.40 0.520.010 0.006 0.17 0.03 5.47 0.58 — — — 0.03

TABLE 3 Overlay welding wire for overlaying (% by weight) Wire Ni + No.C Si Mn P S Cu Ni Cr Mo V Nb Ti Nb + Ti 3 0.10 0.36 0.77 0.006 0.0090.19 0.06 2.29 1.11 0.01 — 0.002 0.06 7 0.12 0.17 0.41 0.003 0.006 0.160.02 2.31 1.06 0.27 0.04 — 0.06 8 0.12 0.53 1.86 0.003 0.002 0.16 0.191.45 0.56 0.01 0.01 — 0.20

TABLE 4 Test Temperature between material Number of Wire preheating andpath Current Voltage Rate Tungsten No. Lamination layers No. (aim) (°C.) (A) (V) (mm/min) aim (mm) TP-1 first layer 1 1 200 230 14 155 lap1.5 TP-2 220 220 14 155 toe aim TP-3 280 250 14 155 toe aim Alloverlaying until 20 mm 8 200-300 240 14 155 toe aim Residual 8 200-300200-240 20-27 120-230 — layer (10 mm)

Then, in order to evaluate the stress relief annealing cracksusceptibility with the Cr amount, a high-temperature low strain ratetensile test was conducted at a strain rate of 6.7×10⁻⁶/s using Crvariation materials in which the Cr content was varied by changingwelding conditions. A value of reduction in area (%) was used for theevaluation.

Table 5 shows results of check analysis of the first layer and FIG. 3shows correlation between the Cr amount and the reduction in areaobtained as a result of the high-temperature low strain rate tensiletest. With an increase in the Cr amount of the first layer weldingsection, the reduction in area increases and the reduction in area wassaturated at about 4.0% of the Cr amount. From the result, it wasrevealed that 4.0% or more is necessary as the Cr amount of the firstlayer welding section.

TABLE 5 Wire First Upper Results of check analysis (% by weight) No.layer No. layer No. C Si Mn P S Ni Cr Cu Mo V TP-1 1 7 0.11 0.42 0.680.011 0.008 0.13 4.99 0.14 0.30 0.10 TP-2 0.10 0.32 0.63 0.006 0.0080.06 2.65 0.17 0.68 0.19 TP-3 0.10 0.67 1.06 0.012 0.012 0.07 1.92 0.220.12 0.04

Next, Table 6 shows results of check analysis of the first layer weldingsection after overlay welding (the remainder being Fe and unavoidableimpurities) and Table 7 shows results of check analysis of the upperlayer welding section (the remainder being Fe and unavoidableimpurities). Moreover, Table 8 shows weld combinations with which thehigh-temperature low strain rate tensile test was performed and testresults thereof.

The check analysis and the high-temperature low strain rate tensile testwere performed in the same manner as mentioned above.

From Table 6, Cr contained in the first layer welding sections accordingto the invention is from 4.0 to 7.7% by weight but the contents of Crare small in the first layer wires Nos. 1, 2, and 5 and thus thecontents fall out of the above range. Moreover, as compared with therange of the Si content contained in the first layer welding sectionsaccording to the invention, the content is small in the first layer wireNo. 2 and, as compared with the range of the V content, the content islarge in the first layer wire No. 5.

In Table 8, since the accumulation of strain into the first layer isthought to be a cause of generation of the stress relief annealingcracks, the case where a test piece was broken at the first layer andthe reduction in area at break is 10% or less is shown as (x), the casewhere a test piece was broken at the first layer and the reduction inarea at break is more than 10% and less than 30% is shown as (Δ), andthe case where a test piece was broken at the upper layer and thereduction in area at break is 30% or more is shown as (0). As isapparent also from Table 8, with wires of Examples which satisfy therequirements of the invention, test pieces are broken at the upper layerwelding metal or the reduction in area at break exceeds 10% even whenthey are broken at the first layer section, so that no accumulation ofstrain into the first layer is observed or a sufficient reduction inarea at break is exhibited even when the accumulation of strain into thefirst layer is observed.

TABLE 6 Wire Results of check analysis of first layer welding section (%by weight) No. C Si Mn P S Cu Ni Cr Mo V Nb W Co B 1 0.10 0.56 0.990.012 0.009 0.18 0.09 2.76 0.17 0.06 0.013 0.50 0.84 0.0023 2 0.05 0.040.36 0.005 <0.003 0.14 0.09 3.42 0.21 0.07 0.020 0.62 1.04 0.0026 3 0.110.27 0.54 0.007 0.008 0.13 0.11 4.46 0.93 0.06 0.019 0.52 0.87 0.0022 40.05 0.40 0.79 0.006 0.008 0.09 0.09 4.27 0.94 0.05 0.020 0.46 0.760.0019 5 0.11 0.14 0.34 0.005 0.006 0.14 0.09 3.89 0.93 0.27 0.046 0.380.64 0.0017 6 0.09 0.32 0.38 0.007 0.006 0.15 0.08 6.53 0.57 0.05 0.0150.41 0.71 0.0015

TABLE 7 Wire Results of check analysis of upper layer welding section (%by weight) No. C Si Mn P S Cu Ni Cr Mo V Nb Ti 3 0.10 0.36 0.75 0.0060.007 0.19 0.06 3.56 1.09 0.02 <0.005 0.002 7 0.10 0.1 0.40 0.005 0.0060.16 0.04 2.27 1.03 0.29 0.04 — 8 0.11 0.54 1.91 0.007 0.004 0.16 0.261.41 0.54 <0.01 <0.005 —

TABLE 8 Second and Results of high- First layer of subsequenttemperature low strain Cr amount of V amount First layer upper layerlayers of upper rate tensile test second layer*2 Pcr(2) (% by wire No.wire No. layer wire No. (reduction in area, %)*1 (% by weight) valueFerrite weight) 1 7 7 x (4.9)  2.42 1.45 ∘ (absence) 0.27 2 x (6.2) 2.62 1.42 ∘ (absence) 0.27 3 Δ (14.4) 2.93 1.37 ∘ (absence) 0.27 4 Δ(13.5) 2.87 1.38 ∘ (absence) 0.27 5 ∘ (48.5) 2.76 1.40 ∘ (absence) 0.271 8 8 ∘ (84.0) 1.82 0.85 ∘ (absence) 0.02 3 ∘ (82.4) 2.33 0.77 ∘(absence) 0.02 4 ∘ (82.0) 2.27 0.77 ∘ (absence) 0.02 5 ∘ (83.1) 2.150.79 ∘ (absence) 0.10 6 ∘ (81.5) 2.95 0.66 Δ (minute)  0.02 6 3 8 ∘(83.4) 3.56 1.27 ∘ (absence) 0.02 *1∘: reduction in area ≧ 30%, Δ: 30% >reduction in area > 10%, x: reduction in area ≦ 10% *2in case wheredilution amount from first layer is regarded as 30% Pcr (2) value:calculation value of first layer of upper layer

In the case where the difference in the Cr amount contained is large asin the case of the first layer welding metal (first layer wire No. 6)and the upper layer welding metal (upper layer wire No. 8), Pcr (2) was0.66 in the following expression and minute ferrite was formed at theboundary of the welding sections. Since ferrite induces a local decreasein strength and there is a possibility of concentration of strain duringthe stress relief annealing treatment. Therefore, it is preferable toprevent the ferrite formation, so that the Cr amount of each layerdesirably satisfies a value larger than 0.7 in the expression shownbelow. Moreover, from the following expression (1), the precipitation offerrite at the boundary between the base material and the first layercan be prevented when the Cr amount of the first layer welding sectionis 4.1% or more.

Pcr(n)=(Cr amount in metal at n-th layer)×0.65−{Cr amount in metal at(n-1)-th layer−Cr amount in metal at n-th layer}×0.35>0.7  (1),

in which n=0 represents the base material and n=1 represents the firstlayer.[0088]

After welding was performed with a welding material for the first layerwelding section where the welding material was selected from Table 2based on the results in Table 8, a ring crack test was conducted, whichis a test for evaluating the stress relief annealing cracksusceptibility of the first layer welding section. FIG. 4 shows a shapeof a ring crack test piece and a sampling position of the test piece.

In FIG. 4( a), 10 is a 12Cr rotor substrate, 11 is a first layer weldingsection, and 12 is a ring crack test piece.

FIG. 4( b) shows a side view of the ring crack test piece 12 and FIG. 4(c) shows a front view of the ring crack test piece 12. FIG. 4( d) is anenlarged view of the A part in FIG. 4( c).

The ring crack test piece 12 has a cylindrical shape having an innerdiameter of 5 mm, an outer diameter of 10 mm, and a length of 20 mm anda slit 12 a running through in a diameter direction and having a gap of0.3 mm is formed along an axis direction in the side wall. Also, on theouter peripheral wall at the opposite side of the slit 12 a, a U notch12 b having a width of 0.4 mm, a depth of 0.5 mm, and a bottom partwhose cross-sectional shape is a curved shape having a curvature of 0.2mm is formed along an axis direction.

In order to exclude the influence of the welding thermal cycle, afterone layer is build up on the base material with an arbitrary weldingmaterial, the ring crack test piece 12 is sampled with adjustment sothat the U notch comes to an unaffected zone, in a welded state withoutfurther treatment (FIG. 4( a)).

By imparting a force to the sampled test piece in arrowed directions asshown in FIG. 5, the slit 12 a was caulked and gathered and thensubjected to TIG welding and restrained, so that tensile residual stresswas imparted to the bottom part of the U notch 12 b.

After the restrained and welded ring crack test piece 121 was subjectedto a stress relief annealing treatment at 630° C.×10 hours, the presenceof cracks was evaluated using two test pieces (N−1, N−2) by observingthree cross-sections per one test piece, i.e., six cross-sections intotal. Table 9 shows the results. Also, the Pcr(1) value was calculatedbased on the expression (1) and shown in Table 9.

The case where no crack is generated was shown as “O” and the case wherecrack(s) were generated was shown as “x”.

Here, the compositions of elements constituting the wires Nos. 3, 4, and6 fall within the range of the first layer welding section according tothe invention and the wires Nos. 1 and 5 have compositions fallingoutside the range of the first layer welding section according to theinvention.

From the results in Table 9, the stress relief annealing cracksusceptibility varied depending on the Cr content and the stress reliefannealing crack susceptibility decreased in the case of a high Crmaterial.

TABLE 9 0.3 mm slit N-1 N-2 Wire Cross-section Cross-sectionCross-section Cross-section Cross-section Cross-section Pcr(1) No. A B CA B C value 1 x x x x x x −0.63 3 ∘ ∘ ∘ ∘ ∘ ∘ 1.06 4 ∘ ∘ ∘ ∘ ∘ ∘ 0.88 5∘ x x ∘ ∘ ∘ 0.49 6 ∘ ∘ ∘ ∘ ∘ ∘ 3.13 ∘: no crack is generated, x:crack(s) were generated

Table 10 shows results collecting the above Examples. In the over-allevaluation, it was evaluated so that the case where all the individualevaluation items were shown as “O” was marked “OO”, the case where “Δ”was present was marked “O”, and the case where “x” was present in anyitem was marked “x”. The case where the over-all evaluation is marked“OO” can be judged to be sufficiently usable and the case where theover-all evaluation is marked “O” can be judged to be usable.

From the results, the welding sections and welding materials accordingto the invention exhibit low stress relief annealing cracksusceptibility of the first layer and no accumulation of strain in thefirst layer was observed in the high-temperature low strain rate tensiletest, so that breakage occurs at the upper layer welding metal.Furthermore, by considering Cr in the base material, the first layer,and the upper layer, the precipitation of ferrite can be alsosuppressed.

TABLE 10 Second and Result of high- Result of ring First layer Firstlayer of subsequent layers temperature low crack test of welding upperlayer of upper layer strain rate first layer Presence of Overall Symbolwire No. welding wire No. welding wire No. tensile test welding metalferrite evaluation Example 1 3 8 8 ∘ ∘ ∘ ∘∘ 2 4 8 8 ∘ ∘ ∘ ∘∘ 3 6 8 8 ∘ ∘Δ ∘ 4 6 3 8 ∘ ∘ ∘ ∘∘ 5 3 7 7 Δ ∘ ∘ ∘ 6 4 7 7 Δ ∘ ∘ ∘ Comparative 1 1 7 7x x ∘ x Example 2 2 7 7 x — ∘ x 3 5 7 7 ∘ x ∘ x 4 1 8 8 ∘ x ∘ x 5 5 8 8∘ x ∘ x

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

The present application is based on Japanese Patent Application No.2011-178628 filed on Aug. 17, 2011, and the contents are incorporatedherein by reference.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   -   1: High Cr steel turbine rotor    -   2: Journal part    -   3: Thrust part    -   10: 12Cr rotor substrate    -   11: First layer welding section    -   12: Ring crack test piece    -   12 a: Slit    -   12 b: U Notch    -   13: Upper layer welding section    -   14: Base material    -   20: Check analysis position    -   100: Restraint welding section (TIG welding/non-filler)    -   121: Restrained and welded ring crack test piece

1. A first layer welding section of a high Cr steel turbine rotor, whichis a first layer welding section among a multilayer overlay weldingsection formed on a bearing contact surface of the high Cr steel turbinerotor, the first layer welding section comprising, in terms of % byweight: C: 0.05 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.5%, Cr: 4.0 to7.7%, and Mo: 0.5 to 1.5%, with a remainder including Fe and unavoidableimpurities, in which the unavoidable impurities contain P: 0.015% orless, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% orless, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less, and Nb:0.07% or less in terms of % by weight based on the first layer weldingsection.
 2. The first layer welding section of the high Cr steel turbinerotor according to claim 1, which satisfies an expression (1):Pcr(1)=(a Cr amount in the first layer welding section)×0.65−(a Cramount of the high Cr steel turbine rotor−the Cr amount in the firstlayer welding section)×0.35>0.7  (1).
 3. An overlay welding material fora first layer welding section of a high Cr steel turbine rotor, which isa welding material for obtaining the first layer welding sectionaccording to claim 1 among the multilayer overlay welding section formedon the bearing contact surface of the high Cr steel turbine rotor, thewelding material comprising, in terms of % by weight: C: 0.03 to 0.2%,Si: 0.1 to 1.0%, Mn: 0.3 to 1.2%, Cr: 2.0 to 5.5%, and Mo: 0.1 to 1.5%,with a remainder including Fe and unavoidable impurities, in which theunavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu:0.2% or less, and V: 0.1% or less, and a sum of one or more kindsselected from the group consisting of Ni, Nb and Ti is 0.2% or less interms of % by weight based on the welding material.
 4. An upper layerwelding section of a high Cr steel turbine rotor, which is an upperlayer welding section formed on the first layer welding sectionaccording to claim 1, among the multilayer overlay welding sectionformed on the bearing contact surface of the high Cr steel turbinerotor, the upper layer welding section comprising, in terms of % byweight: C: 0.05 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 2.5%, Cr: 1.0 to4.0%, and Mo: 0.5 to 1.5%, with a remainder including Fe and unavoidableimpurities, in which the unavoidable impurities contain P: 0.015% orless, S: 0.015% or less, Cu: 0.2% or less, V: 0.15% or less, Ni: 0.3% orless, and Nb: 0.07% or less in terms of % by weight based on the upperlayer welding section.
 5. The upper layer welding section of the high Crsteel turbine rotor according to claim 4, wherein an amount of Vcontained in the upper layer welding section is smaller than an amountof V contained in the first layer welding section.
 6. The upper layerwelding section of the high Cr steel turbine rotor according to claim 4,which satisfies an expression (2):Pcr(n)=(a Cr amount in the upper layer welding section at n-thlayer)×0.65−{a Cr amount in the upper layer welding section at (n−1)-thlayer−the Cr amount in the upper layer welding section at the n-thlayer}×0.35>0.7  (2), in which when N represents the number of layersconstituting the multilayer overlay welding section, 2≦n≦N.
 7. Anoverlay welding material for an upper layer welding section of a high Crsteel turbine rotor, which is a welding material for obtaining the upperlayer welding section according to claim 4 formed on the first layerwelding section of the multilayer overlay welding section formed on thebearing contact surface of the high Cr steel turbine rotor, the weldingmaterial comprising, in terms of % by weight: C: 0.03 to 0.2%, Si: 0.1to 1.0%, Mn: 0.3 to 3.0%, Cr: 1.0 to 2.5%, and Mo: 0.1 to 1.5%, with aremainder including Fe and unavoidable impurities, in which theunavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu:0.2% or less, and V: 0.1% or less, and a sum of one or more kindsselected from the group consisting of Ni, Nb and Ti is 0.2% or less interms of % by weight based on the welding material.
 8. A process forproducing a multilayer overlay welding section of a high Cr steelturbine rotor, the process comprising: forming a first layer weldingsection of a high Cr steel turbine rotor, which is a first layer weldingsection among a multilayer overlay welding section formed on a bearingcontact surface of the high Cr steel turbine rotor, the first layerwelding section comprising, in terms of % by weight: C: 0.05 to 0.2%,Si: 0.1 to 1.0%, Mn: 0.3 to 1.5%, Cr: 4.0 to 7.7%, and Mo: 0.5 to 1.5%,with a remainder including Fe and unavoidable impurities, in which theunavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu:0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B:0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of % byweight based on the first layer welding section, on the bearing contactsurface of the high Cr steel turbine rotor by welding using an overlaywelding material for the first layer welding section comprising, interms of % by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.2%,Cr: 2.0 to 5.5%, and Mo: 0.1 to 1.5%, with a remainder including Fe andunavoidable impurities, in which the unavoidable impurities contain P:0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% orless, and a sum of one or more kinds selected from the group consistingof Ni, Nb and Ti is 0.2% or less in terms of % by weight based on theoverlay welding material for the first layer welding section, andforming the upper layer welding section according to claim 4 on an upperlayer of the thus-formed first layer welding section by welding using anoverlay welding material for the upper layer welding section comprising,in terms of % by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to3.0%, Cr: 1.0 to 2.5%, and Mo: 0.1 to 1.5%, with a remainder includingFe and unavoidable impurities, in which the unavoidable impuritiescontain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V:0.1% or less, and a sum of one or more kinds selected from the groupconsisting of Ni, Nb and Ti is 0.2% or less in terms of % by weightbased on the overlay welding material for the upper layer weldingsection.
 9. The upper layer welding section of the high Cr steel turbinerotor according to claim 5, which satisfies an expression (2):Pcr(n)=(a Cr amount in the upper layer welding section at n-thlayer)×0.65−{a Cr amount in the upper layer welding section at (n−1)-thlayer−the Cr amount in the upper layer welding section at the n-thlayer}×0.35>0.7  (2), in which when N represents the number of layersconstituting the multilayer overlay welding section, 2≦n≦N.
 10. Anoverlay welding material for an upper layer welding section of a high Crsteel turbine rotor, which is a welding material for obtaining the upperlayer welding section according to claim 5 formed on the first layerwelding section of the multilayer overlay welding section formed on thebearing contact surface of the high Cr steel turbine rotor, the weldingmaterial comprising, in terms of % by weight: C: 0.03 to 0.2%, Si: 0.1to 1.0%, Mn: 0.3 to 3.0%, Cr: 1.0 to 2.5%, and Mo: 0.1 to 1.5%, with aremainder including Fe and unavoidable impurities, in which theunavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu:0.2% or less, and V: 0.1% or less, and a sum of one or more kindsselected from the group consisting of Ni, Nb and Ti is 0.2% or less interms of % by weight based on the welding material.
 11. An overlaywelding material for an upper layer welding section of a high Cr steelturbine rotor, which is a welding material for obtaining the upper layerwelding section according to claim 6 formed on the first layer weldingsection of the multilayer overlay welding section formed on the bearingcontact surface of the high Cr steel turbine rotor, the welding materialcomprising, in terms of % by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%,Mn: 0.3 to 3.0%, Cr: 1.0 to 2.5%, and Mo: 0.1 to 1.5%, with a remainderincluding Fe and unavoidable impurities, in which the unavoidableimpurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% orless, and V: 0.1% or less, and a sum of one or more kinds selected fromthe group consisting of Ni, Nb and Ti is 0.2% or less in terms of % byweight based on the welding material.
 12. An overlay welding materialfor an upper layer welding section of a high Cr steel turbine rotor,which is a welding material for obtaining the upper layer weldingsection according to claim 9 formed on the first layer welding sectionof the multilayer overlay welding section formed on the bearing contactsurface of the high Cr steel turbine rotor, the welding materialcomprising, in terms of % by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%,Mn: 0.3 to 3.0%, Cr: 1.0 to 2.5%, and Mo: 0.1 to 1.5%, with a remainderincluding Fe and unavoidable impurities, in which the unavoidableimpurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% orless, and V: 0.1% or less, and a sum of one or more kinds selected fromthe group consisting of Ni, Nb and Ti is 0.2% or less in terms of % byweight based on the welding material.
 13. A process for producing amultilayer overlay welding section of a high Cr steel turbine rotor, theprocess comprising: forming a first layer welding section of a high Crsteel turbine rotor, which is a first layer welding section among amultilayer overlay welding section formed on a bearing contact surfaceof the high Cr steel turbine rotor, the first layer welding sectioncomprising, in terms of % by weight: C: 0.05 to 0.2%, Si: 0.1 to 1.0%,Mn: 0.3 to 1.5%, Cr: 4.0 to 7.7%, and Mo: 0.5 to 1.5%, with a remainderincluding Fe and unavoidable impurities, in which the unavoidableimpurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% orless, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% orless, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weightbased on the first layer welding section, on the bearing contact surfaceof the high Cr steel turbine rotor by welding using an overlay weldingmaterial for the first layer welding section comprising, in terms of %by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.2%, Cr: 2.0 to5.5%, and Mo: 0.1 to 1.5%, with a remainder including Fe and unavoidableimpurities, in which the unavoidable impurities contain P: 0.015% orless, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and asum of one or more kinds selected from the group consisting of Ni, Nband Ti is 0.2% or less in terms of % by weight based on the overlaywelding material for the first layer welding section, and forming theupper layer welding section according to claim 5 on an upper layer ofthe thus-formed first layer welding section by welding using an overlaywelding material for the upper layer welding section comprising, interms of % by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 3.0%,Cr: 1.0 to 2.5%, and Mo: 0.1 to 1.5%, with a remainder including Fe andunavoidable impurities, in which the unavoidable impurities contain P:0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% orless, and a sum of one or more kinds selected from the group consistingof Ni, Nb and Ti is 0.2% or less in terms of % by weight based on theoverlay welding material for the upper layer welding section.
 14. Aprocess for producing a multilayer overlay welding section of a high Crsteel turbine rotor, the process comprising: forming a first layerwelding section of a high Cr steel turbine rotor, which is a first layerwelding section among a multilayer overlay welding section formed on abearing contact surface of the high Cr steel turbine rotor, the firstlayer welding section comprising, in terms of % by weight: C: 0.05 to0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.5%, Cr: 4.0 to 7.7%, and Mo: 0.5 to1.5%, with a remainder including Fe and unavoidable impurities, in whichthe unavoidable impurities contain P: 0.015% or less, S: 0.015% or less,Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less,B: 0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of %by weight based on the first layer welding section, on the bearingcontact surface of the high Cr steel turbine rotor by welding using anoverlay welding material for the first layer welding section comprising,in terms of % by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to1.2%, Cr: 2.0 to 5.5%, and Mo: 0.1 to 1.5%, with a remainder includingFe and unavoidable impurities, in which the unavoidable impuritiescontain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V:0.1% or less, and a sum of one or more kinds selected from the groupconsisting of Ni, Nb and Ti is 0.2% or less in terms of % by weightbased on the overlay welding material for the first layer weldingsection, and forming the upper layer welding section according to claim6 on an upper layer of the thus-formed first layer welding section bywelding using an overlay welding material for the upper layer weldingsection comprising, in terms of % by weight: C: 0.03 to 0.2%, Si: 0.1 to1.0%, Mn: 0.3 to 3.0%, Cr: 1.0 to 2.5%, and Mo: 0.1 to 1.5%, with aremainder including Fe and unavoidable impurities, in which theunavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu:0.2% or less, and V: 0.1% or less, and a sum of one or more kindsselected from the group consisting of Ni, Nb and Ti is 0.2% or less interms of % by weight based on the overlay welding material for the upperlayer welding section.
 15. A process for producing a multilayer overlaywelding section of a high Cr steel turbine rotor, the processcomprising: forming a first layer welding section of a high Cr steelturbine rotor, which is a first layer welding section among a multilayeroverlay welding section formed on a bearing contact surface of the highCr steel turbine rotor, the first layer welding section comprising, interms of % by weight: C: 0.05 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.5%,Cr: 4.0 to 7.7%, and Mo: 0.5 to 1.5%, with a remainder including Fe andunavoidable impurities, in which the unavoidable impurities contain P:0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less,Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less,and Nb: 0.07% or less in terms of % by weight based on the first layerwelding section, on the bearing contact surface of the high Cr steelturbine rotor by welding using an overlay welding material for the firstlayer welding section comprising, in terms of % by weight: C: 0.03 to0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.2%, Cr: 2.0 to 5.5%, and Mo: 0.1 to1.5%, with a remainder including Fe and unavoidable impurities, in whichthe unavoidable impurities contain P: 0.015% or less, S: 0.015% or less,Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kindsselected from the group consisting of Ni, Nb and Ti is 0.2% or less interms of % by weight based on the overlay welding material for the firstlayer welding section, and forming the upper layer welding sectionaccording to claim 9 on an upper layer of the thus-formed first layerwelding section by welding using an overlay welding material for theupper layer welding section comprising, in terms of % by weight: C: 0.03to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 3.0%, Cr: 1.0 to 2.5%, and Mo: 0.1to 1.5%, with a remainder including Fe and unavoidable impurities, inwhich the unavoidable impurities contain P: 0.015% or less, S: 0.015% orless, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or morekinds selected from the group consisting of Ni, Nb and Ti is 0.2% orless in terms of % by weight based on the overlay welding material forthe upper layer welding section.
 16. A process for producing amultilayer overlay welding section of a high Cr steel turbine rotor, theprocess comprising: forming a first layer welding section of a high Crsteel turbine rotor, which is a first layer welding section among amultilayer overlay welding section formed on a bearing contact surfaceof the high Cr steel turbine rotor, the first layer welding sectioncomprising, in terms of % by weight: C: 0.05 to 0.2%, Si: 0.1 to 1.0%,Mn: 0.3 to 1.5%, Cr: 4.0 to 7.7%, and Mo: 0.5 to 1.5%, with a remainderincluding Fe and unavoidable impurities, in which the unavoidableimpurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% orless, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% orless, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weightbased on the first layer welding section, on the bearing contact surfaceof the high Cr steel turbine rotor by welding using an overlay weldingmaterial for the first layer welding section comprising, in terms of %by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.2%, Cr: 2.0 to5.5%, and Mo: 0.1 to 1.5%, with a remainder including Fe and unavoidableimpurities, in which the unavoidable impurities contain P: 0.015% orless, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and asum of one or more kinds selected from the group consisting of Ni, Nband Ti is 0.2% or less in terms of % by weight based on the overlaywelding material for the first layer welding section, and forming theupper layer welding section according to claim 7 on an upper layer ofthe thus-formed first layer welding section by welding using an overlaywelding material for the upper layer welding section comprising, interms of % by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 3.0%,Cr: 1.0 to 2.5%, and Mo: 0.1 to 1.5%, with a remainder including Fe andunavoidable impurities, in which the unavoidable impurities contain P:0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% orless, and a sum of one or more kinds selected from the group consistingof Ni, Nb and Ti is 0.2% or less in terms of % by weight based on theoverlay welding material for the upper layer welding section.
 17. Aprocess for producing a multilayer overlay welding section of a high Crsteel turbine rotor, the process comprising: forming a first layerwelding section of a high Cr steel turbine rotor, which is a first layerwelding section among a multilayer overlay welding section formed on abearing contact surface of the high Cr steel turbine rotor, the firstlayer welding section comprising, in terms of % by weight: C: 0.05 to0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.5%, Cr: 4.0 to 7.7%, and Mo: 0.5 to1.5%, with a remainder including Fe and unavoidable impurities, in whichthe unavoidable impurities contain P: 0.015% or less, S: 0.015% or less,Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less,B: 0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of %by weight based on the first layer welding section, on the bearingcontact surface of the high Cr steel turbine rotor by welding using anoverlay welding material for the first layer welding section comprising,in terms of % by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to1.2%, Cr: 2.0 to 5.5%, and Mo: 0.1 to 1.5%, with a remainder includingFe and unavoidable impurities, in which the unavoidable impuritiescontain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V:0.1% or less, and a sum of one or more kinds selected from the groupconsisting of Ni, Nb and Ti is 0.2% or less in terms of % by weightbased on the overlay welding material for the first layer weldingsection, and forming the upper layer welding section according to claim10 on an upper layer of the thus-formed first layer welding section bywelding using an overlay welding material for the upper layer weldingsection comprising, in terms of % by weight: C: 0.03 to 0.2%, Si: 0.1 to1.0%, Mn: 0.3 to 3.0%, Cr: 1.0 to 2.5%, and Mo: 0.1 to 1.5%, with aremainder including Fe and unavoidable impurities, in which theunavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu:0.2% or less, and V: 0.1% or less, and a sum of one or more kindsselected from the group consisting of Ni, Nb and Ti is 0.2% or less interms of % by weight based on the overlay welding material for the upperlayer welding section.
 18. A process for producing a multilayer overlaywelding section of a high Cr steel turbine rotor, the processcomprising: forming a first layer welding section of a high Cr steelturbine rotor, which is a first layer welding section among a multilayeroverlay welding section formed on a bearing contact surface of the highCr steel turbine rotor, the first layer welding section comprising, interms of % by weight: C: 0.05 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.5%,Cr: 4.0 to 7.7%, and Mo: 0.5 to 1.5%, with a remainder including Fe andunavoidable impurities, in which the unavoidable impurities contain P:0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less,Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less,and Nb: 0.07% or less in terms of % by weight based on the first layerwelding section, on the bearing contact surface of the high Cr steelturbine rotor by welding using an overlay welding material for the firstlayer welding section comprising, in terms of % by weight: C: 0.03 to0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.2%, Cr: 2.0 to 5.5%, and Mo: 0.1 to1.5%, with a remainder including Fe and unavoidable impurities, in whichthe unavoidable impurities contain P: 0.015% or less, S: 0.015% or less,Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kindsselected from the group consisting of Ni, Nb and Ti is 0.2% or less interms of % by weight based on the overlay welding material for the firstlayer welding section, and forming the upper layer welding sectionaccording to claim 11 on an upper layer of the thus-formed first layerwelding section by welding using an overlay welding material for theupper layer welding section comprising, in terms of % by weight: C: 0.03to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 3.0%, Cr: 1.0 to 2.5%, and Mo: 0.1to 1.5%, with a remainder including Fe and unavoidable impurities, inwhich the unavoidable impurities contain P: 0.015% or less, S: 0.015% orless, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or morekinds selected from the group consisting of Ni, Nb and Ti is 0.2% orless in terms of % by weight based on the overlay welding material forthe upper layer welding section.
 19. A process for producing amultilayer overlay welding section of a high Cr steel turbine rotor, theprocess comprising: forming a first layer welding section of a high Crsteel turbine rotor, which is a first layer welding section among amultilayer overlay welding section formed on a bearing contact surfaceof the high Cr steel turbine rotor, the first layer welding sectioncomprising, in terms of % by weight: C: 0.05 to 0.2%, Si: 0.1 to 1.0%,Mn: 0.3 to 1.5%, Cr: 4.0 to 7.7%, and Mo: 0.5 to 1.5%, with a remainderincluding Fe and unavoidable impurities, in which the unavoidableimpurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% orless, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% orless, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weightbased on the first layer welding section, on the bearing contact surfaceof the high Cr steel turbine rotor by welding using an overlay weldingmaterial for the first layer welding section comprising, in terms of %by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.2%, Cr: 2.0 to5.5%, and Mo: 0.1 to 1.5%, with a remainder including Fe and unavoidableimpurities, in which the unavoidable impurities contain P: 0.015% orless, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and asum of one or more kinds selected from the group consisting of Ni, Nband Ti is 0.2% or less in terms of % by weight based on the overlaywelding material for the first layer welding section, and forming theupper layer welding section according to claim 12 on an upper layer ofthe thus-formed first layer welding section by welding using an overlaywelding material for the upper layer welding section comprising, interms of % by weight: C: 0.03 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 3.0%,Cr: 1.0 to 2.5%, and Mo: 0.1 to 1.5%, with a remainder including Fe andunavoidable impurities, in which the unavoidable impurities contain P:0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% orless, and a sum of one or more kinds selected from the group consistingof Ni, Nb and Ti is 0.2% or less in terms of % by weight based on theoverlay welding material for the upper layer welding section.